Rock-eating mycorrhizas: their role in plant nutrition and biogeochemical cycles

A decade ago, tunnels inside mineral grains were found that were likely formed by hyphae of ectomycorrhizal (EcM) fungi. This observation implied that EcM fungi can dissolve mineral grains. The observation raised several questions on the ecology of these ¿rock-eating¿ fungi. This review addresses the roles of these rock-eating EcM associations in plant nutrition, biogeochemical cycles and pedogenesis. Research approaches ranged from molecular to ecosystem level scales. Nutrient deficiencies change EcM seedling exudation patterns of organic anions and thus their potential to mobilise base cations from minerals. This response was fungal species-specific. Some EcM fungi accelerated mineral weathering. While mineral weathering could also increase the concentrations of phytotoxic aluminium in the soil solution, some EcM fungi increase Al tolerance through an enhanced exudation of oxalate. Through their contribution to Al transport, EcM hyphae could be agents in pedogenesis, especially podzolisation. A modelling study indicated that mineral tunnelling is less important than surface weathering by EcM fungi. With both processes taken together, the contribution of EcM fungi to weathering may be significant. In the field vertical niche differentiation of EcM fungi was shown for EcM root tips and extraradical mycelium. In the field EcM fungi and tunnel densities were correlated. Our results support a role of rock-eating EcM fungi in plant nutrition and biogeochemical cycles. EcM fungal species-specific differences indicate the need for further research with regard to this variation in functional traits

Simulation of junctionless Si nanowire transistors with 3 nm gate length

Inspired by recent experimental realizations and theoretical simulations of thin silicon nanowire-based devices, we perform proof-of-concept simulations of junctionless gated Si nanowire transistors. Based on first-principles, our primary predictions are that Si-based transistors are physically possible without major changes in design philosophy at scales of similar to 1 nm wire diameter and similar to 3 nm gate length, and that the junctionless transistor avoids potentially serious difficulties affecting junctioned channels at these length scales. We also present investigations into atomic-level design factors such as dopant positioning and concentration. (C) 2010 American Institute of Physics. (doi:10.1063/1.3478012

A nanomechanical resonator shuttling single electrons at radio frequencies

We observe transport of electrons through a metallic island on the tip of a nanomechanical pendulum. The resulting tunneling current shows distinct features corresponding to the discrete mechanical eigenfrequencies of the pendulum. We report on measurements covering the temperature range from 300 K down to 4.2 K. We explain the I-V curve, which differs from previous theoretical predictions, with model calculations based on a Master equation approach.Comment: 5 pages, 4 jpeg-figure

Genome-wide diversity and gene expression profiling of Babesia microti isolates identify polymorphic genes that mediate host-pathogen interactions

Babesia microti, a tick-transmitted, intraerythrocytic protozoan parasite circulating mainly among small mammals, is the primary cause of human babesiosis. While most cases are transmitted by Ixodes ticks, the disease may also be transmitted through blood transfusion and perinatally. A comprehensive analysis of genome composition, genetic diversity, and gene expression profiling of seven B. microti isolates revealed that genetic variation in isolates from the Northeast United States is almost exclusively associated with genes encoding the surface proteome and secretome of the parasite. Furthermore, we found that polymorphism is restricted to a small number of genes, which are highly expressed during infection. In order to identify pathogen-encoded factors involved in host-parasite interactions, we screened a proteome array comprised of 174 B. microti proteins, including several predicted members of the parasite secretome. Using this immuno-proteomic approach we identified several novel antigens that trigger strong host immune responses during the onset of infection. The genomic and immunological data presented herein provide the first insights into the determinants of B. microti interaction with its mammalian hosts and their relevance for understanding the selective pressures acting on parasite evolution

Numerical analysis and simulation of the dynamics of mountain glaciers

In this chapter, we analyze and approximate a nonlinear stationary Stokes problem that describes the motion of glacier ice. The existence and uniqueness of solutions are proved and an a priori error estimate for the finite element approximation is found. In a second time, we combine the Stokes problem with a transport equation for the volume fraction of ice, which describes the time evolution of a glacier. The accumulation due to snow precipitation and melting are accounted for in the source term of the transport equation. A decoupling algorithm allows the diffusion and the advection problems to be solved using a two-grids method. As an illustration, we simulate the evolution of Aletsch glacier, Switzerland, over the 21st century by using realistic climatic conditions

Determining the electronic performance limitations in top-down fabricated Si nanowires with mean widths down to 4 nm

Silicon nanowires have been patterned with mean widths down to 4 nm using top-down lithography and dry etching. Performance-limiting scattering processes have been measured directly which provide new insight into the electronic conduction mechanisms within the nanowires. Results demonstrate a transition from 3-dimensional (3D) to 2D and then 1D as the nanowire mean widths are reduced from 12 to 4 nm. The importance of high quality surface passivation is demonstrated by a lack of significant donor deactivation, resulting in neutral impurity scattering ultimately limiting the electronic performance. The results indicate the important parameters requiring optimization when fabricating nanowires with atomic dimensions

One-dimensional Weak Localization of Electrons in a Single InAs Nanowire

We report on low temperature (2-30K) electron transport and magneto-transport measurements of a chemically synthesized InAs nanowire. Both the temperature, T, and transverse magnetic field dependences of the nanowire conductance are consistent with the functional forms predicted in one-dimensional (1D) weak localization theory. By fitting the magneto-conductance data to theory, the phase coherence length of electrons is determined to be tens of nanometers with a T-1/3 dependence. Moreover, as the electron density is increased by a gate voltage, the magneto-conductance shows a possible signature of suppression of weak localization in multiple 1D subbands

Clinical significance of genetic aberrations in secondary acute myeloid leukemia

The study aimed to identify genetic lesions associated with secondary acute myeloid leukemia (sAML) in comparison with AML arising de novo (dnAML) and assess their impact on patients' overall survival (OS). High-resolution genotyping and loss of heterozygosity mapping was performed on DNA samples from 86 sAML and 117 dnAML patients, using Affymetrix Genome-Wide Human SNP 6.0 arrays. Genes TP53, RUNX1, CBL, IDH1/2, NRAS, NPM1, and FLT3 were analyzed for mutations in all patients. We identified 36 recurrent cytogenetic aberrations (more than five events). Mutations in TP53, 9pUPD, and del7q (targeting CUX1 locus) were significantly associated with sAML, while NPM1 and FLT3 mutations associated with dnAML. Patients with sAML carrying TP53 mutations demonstrated lower 1-year OS rate than those with wild-type TP53 (14.3% +/- 9.4% vs. 35.4% +/- 7.2%; P = 0.002), while complex karyotype, del7q (CUX1) and del7p (IKZF1) showed no significant effect on OS. Multivariate analysis confirmed that mutant TP53 was the only independent adverse prognostic factor for OS in sAML (hazard ratio 2.67; 95% CI: 1.335.37; P = 0.006). Patients with dnAML and complex karyotype carried sAML-associated defects (TP53 defects in 54.5%, deletions targeting FOXP1 and ETV6 loci in 45.4% of the cases). We identified several co-occurring lesions associated with either sAML or dnAML diagnosis. Our data suggest that distinct genetic lesions drive leukemogenesis in sAML. High karyotype complexity of sAML patients does not influence OS. Somatic mutations in TP53 are the only independent adverse prognostic factor in sAML. Patients with dnAML and complex karyotype show genetic features associated with sAML and myeloproliferative neoplasms. Am. J. Hematol., 2012